The invention relates to a device for mixing two pasty substances which are in particular a dental impression substance and a catalyst substance for accelerating polymerization of the dental impression substance.
The device according to the invention is attached onto the two outlet stubs of a discharge device, via which the pasty substances are fed to the mixing device by application of pressure, and after mixing in the mixing device the pasty substances are discharged in the form of a mixture.
In several technical applications it is necessary to apply two separately stored pasty substances in form of a mixture. For this purpose either dynamical or statical continuous mixers are used which mix the substances with each other when the pasty substances flow through a mixer housing. A dynamical mixer is known from EP-A-0 492 412. This known device comprises an essentially tubular mixer housing with a mixer shaft rotatably arranged therein. The mixer shaft comprises a plurality of radially protruding web-shaped mixer elements which, when the mixer shaft is driven, serve for deflection of the substance flows thus mixing the two pasty substances with each other. The pasty substances are fed via a radial front wall at the rear end of the mixer housing into the latter. For this purpose the front wall comprises two inlet stubs which are attached onto the outlet stubs of a device for discharging the pasty substances.
To prevent contamination in the direction of the outlet stubs of the discharge device the known mixer comprises stripping elements protruding from the mixer shaft, the stripping elements moving along the inner side of the rear-side front wall and transporting pasty material entering via the inlet stubs to the side. The pasty material supplied via one of the inlet stubs inside the housing is at least partially transported in circumferential direction by said strippers thus being fed to the area of the other inlet stub where contamination in the direction of the inlet stub and further in the direction of the outlet stub of the respective discharge device connected with the inlet stub may occur when the dynamic mixer is not driven.
It is an object of the invention to provide a device for mixing two pasty substances where the risk of contamination in backward direction is reduced.
To solve this object the invention suggests a device for mixing two pasty substances, the device comprising
a housing comprising an essentially tubular section having two radial inlet openings for the two pasty substances at the rear end and an outlet opening for the mixed pasty substances at the front end of the tubular section,
a driveable mixer shaft extending through the tubular section and rotatably supported in the housing,
wherein the mixer shaft comprises a plurality of rigid mixer elements protruding from an axis, the mixer elements serving for mixing the two pasty substances during their passage through the tubular section of the housing.
According to the invention said device is characterized in that the mixer shaft comprises at the level of the inlet openings at least one deflection element for promoting the transport in axial direction of the pasty substances fed through the inlet openings to the tubular section of the housing, wherein the at least one deflection element comprises a deflection surface extending about the axis and at an inclination to a radial plane of the axis.
In the mixing device according to the invention (hereinafter referred to as dynamic mixer) the pasty substances to be mixed are radially supplied to the essentially tubular section of the mixer housing. For this purpose the tubular section of the housing is provided with two radial inlet openings in particular arranged diametrically opposite each other. The pasty substance flows fed to the mixer by application of pressure are supplied within the tubular section of the housing to at least one deflection element which extends about the axis of the mixer shaft. Said deflection element rotates together with the rotating mixer shaft and comprises a deflection surface extending at an inclination to a radial plane of the axis. In other words, the at least one deflection element is an essentially saw-tooth wedge extending in an arcuate manner about the axis of the mixer shaft. Said deflection element acts in the same way as a screw conveyor in a screw-type pump and ensures that the incoming pasty material is directly transported in axial direction from the inlet openings towards the outlet opening. This reliably prevents contamination in backward direction since the at least one deflection element always promotes the axial transport of the pasty substances fed through the inlet openings to the tubular section of the mixer housing.
As already said above, the deflection element can be of wedge-type configuration. Alternatively to this wedge form the deflection element can be designed as a web extending helically about the axis; in this embodiment the deflection element is configured as a thread. Such helical webs are known from screw-type pumps and screw conveyors.
Advantageously, at the level of the radial inlet openings of the tubular section of the housing two deflection elements are provided on the axis, the deflection elements appropriately being arranged diametrically opposite each other. Said deflection elements or each deflection element preferably extends over an angular range of 180xc2x0 to 90xc2x0.
To be able to attach the dynamic mixer according to the invention onto the two outlet stubs of a squeezing device, the housing comprises at its rear end an insertion part oriented at an inclination to the axis, on which insertion part two inlet stubs are protrudingly arranged. Said insertion part is located in a flared housing section of the mixer joining the tubular section, and comprises two ducts extending from the inlet stub. Said two ducts radially extend, at an angle, to a central cylindrical deepened reception portion on the inner side of the insertion part, which deepened portion receives the axis of the mixer shaft with the at least one deflection element. Thus the cylindrical deepened reception portion of the insertion part forms a portion of the tubular housing section of the mixer.
According to a preferred aspect of the invention a plurality of mixer elements are located between the radial inlet openings and the axial outlet opening within the tubular housing section, said mixer elements protruding in the form of radial webs from the axis and extending up to near the inner surfaces of the tubular housing section. Within several radial planes said mixer elements are arranged such that they protrude from the shaft, which results in deflection of substance flows axially extending through the housing. This leads to the desired mixing effect. The mixing effect is intensified when said mixer elements, which prevent direct flow between the inlet openings and the outlet opening due to their radial orientation, extend over a larger angular range, e.g. 90xc2x0. This can be realized by connecting adjacent mixer elements via a circumferential portion. In this way, mixer elements in the form of quarter circles are configured, wherein it may be of advantage if the middle sections of these quarter circles, as seen in circumferential direction, protrude from the inner surface of the tubular section of the housing to a larger extent than their ends. It is appropriate if two adjacent radially extending mixer elements staggered from radial plane to radial plane, as seen in circumferential direction, are connected with each other in the manner described above.
Besides arrangement of the rigid mixer elements as described above it is of advantage with regard to the mixing process if the mixer shaft comprises additional flexible stripper elements which move along the inner wall of the tubular housing due to their flexible configuration or at least due their flexible free ends arranged at a distance to the axis. Hereunder an embodiment of the invention is explained in detail with reference to the drawings in which: